Biomedical finger assembly with ratcheting lock

ABSTRACT

This disclosure provides systems, apparatuses, and devices for a prosthetic digit usable with persons with amputations at or proximal to the metacarpophalangeal joint. The device restores prehension in a person with missing fingers or thumb by providing opposition to forces in the extension direction via a spring-loaded pawl and locking rack ratchet mechanism, thereby allowing an individual to manipulate or stabilize objects. The digit may be spring-loaded in the extension direction by a torsion spring or other biasing member. The pawl may be automatically disengaged from the rack when the digit reaches full flexion, and the full flexion disengage stop may be adjustable. The pawl may be automatically engaged with the rack when the digit reaches full extension, and the extension stop may be adjustable. The pawl may contain a lateral feature that creates interference with the anchoring linkage under load and limits deflection of the structure.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.17/028,792, filed Sep. 22, 2020, and claims priority to U.S. ProvisionalPatent Application No. 62/904,506, filed Sep. 23, 2019, both of whichare hereby incorporated by reference in their entirety.

TECHNICAL FIELD

The present technology generally relates to an adjustable prosthesis toreplace finger(s) or a thumb at or proximal to the metacarpophalangealjoint.

BACKGROUND

Partial hand loss is the most common upper extremity amputation and hashistorically been underserved by conventional treatment. Most partialhand amputations are traumatic in origin, and many amputations occur inworkplaces where manual labor is performed. Partial hand loss alters theability to sort mail, play an instrument, return to a vocation, or evendress oneself and cut or hold food. The injury is so devastating thatmanual laborers are often unable to return to the same line of work.

The primary goal of functional partial hand prosthetic intervention isto restore opposition grasp: a sufficiently forceful grasp between thethumb and the fingers such that objects can be stabilized andmanipulated. Conventional technology, however, has struggled to providerestorative interventions because of the wide range of anatomical andfunctional presentations post-amputation, and the complexity ofreplacing a powerful, dexterous, and small portion of the human hand.Partial hand loss includes any amputation distal to or through thecarpal bones, including finger loss. Within this definition, fourdistinct zones can be considered: (1) distal to the metacarpophalangealjoint (MCP, or “knuckle”); (2) at or proximal to the MCP joint, butdistal to the carpal bones (transmetacarpal); (3) at the carpal bones;and (4) thenar (full or partial thumb).

Available prosthetic interventions for transmetacarpal partial handamputees can be broadly divided into three categories: (1) cosmeticrestoration; (2) passive prostheses; and (3) driven (active) prostheses.Cosmetic restoration describes a realistic silicone restoration meant toresemble the original anatomy, which almost exclusively providepsychosocial support for the individual, with very little functionalcapability. While invaluable in the rehabilitation process, cosmeticrestorations are often abandoned within a few years.

Passive prostheses are devices which are not actively driven. Theseprostheses can be task-specific end-effectors, such as a grip shaped tofit onto a bicycle handlebar, which are donned and doffed for particularactivities. The passive prostheses also include fixed posts that restoreopposition grasp in the hand, either between a fixed-post thumb andintact fingers, or an intact thumb and fixed fingers. In recent years,this passive category has expanded to include adjustable oppositionsystems. These devices typically replace digits, and have one, two, orthree joints mimicking the MCP, PIP, and DIP joints. The devices canalso be applied to a socket on any upper limb amputation, such as an endeffector for a mechanism (e.g., applied to a transradial amputation).They are spring loaded and adjustable to several postures representingdifferent angles of digit orientation. Due to their robust nature andsimplicity, passive prostheses are often the most utilized choice forreturn to work in manual labor environments.

Active prostheses can be powered by the body or by electricity.Body-powered devices are typically operated by a more proximal intactjoint via linkages, cables, or straps. Some systems use cables runacross the wrist joint to actuate artificial fingers in response towrist flexion. One exemplary partial hand system uses a shoulder harnessto drive fingers or a thumb in an open/close fashion. Electric partialhand solutions usually have individually motorized fingers and rely on abattery pack mounted on the forearm and myoelectric signals to generateseveral hand grasps with the fingers. One drawback of these systems isinhibition of wrist motion and sensitivity to moisture. Bothbody-powered and electrically driven partial hand systems havehistorically been restricted in their use environments due to weakforces and sensitive componentry.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the present technology can be better understood withreference to the following drawings. The components in the drawings arenot necessarily drawn to scale. Instead, emphasis is placed onillustrating clearly the principles of the present technology.Furthermore, components can be shown as transparent in certain views forclarity of illustration only and not to indicate that the component isnecessarily transparent. Components may also be shown schematically.

FIGS. 1A and 1B show elevation and perspective views, respectively, of athree-segment prosthetic digit configured in accordance with anembodiment of the present technology.

FIGS. 2A-2C show elevation, cross-section, and perspective views,respectively, of the three-segment prosthetic digit of FIGS. 1A and 1B,shown at full extension.

FIGS. 2D and 2E show elevation views of rotational connections ofproximal and distal four-bar linkages, respectively, of thethree-segment prosthetic digit of FIGS. 1A and 1B.

FIGS. 3A-3C show perspective, elevation, and cross-section views,respectively, of the prosthetic digit of FIGS. 1A and 1B, shown a fullflexion.

FIGS. 4A and 4B show elevation views of two-segment prosthetic digitconfigured in accordance with another embodiment of the presenttechnology.

DETAILED DESCRIPTION A. Overview

The present technology is directed to a prosthesis digit configured toreplace a finger or thumb. Among other uses, the prosthesis is generallydesigned to provide adjustability, strength, and rigid opposition to adriven thumb or finger (intact or prosthetic). As explained in greaterdetail below, the prosthesis can be adjusted to multiple positions,representing increasing flexion of the digit, and is controlled by theinteraction between a spring-loaded pawl and a rack with multiple teeth.In the illustrated embodiments, the prosthesis is shown having a racklocated in a first segment and having ten positions corresponding toteeth of the rack; however, the rack can be located in other segments ofthe prosthesis (e.g., the second segment, the third segment, etc.) andcan have any number of adjustment positions. When the digit is moved inflexion, the pawl moves freely over the rack teeth in the flexiondirection, but is halted in the extension direction by the engagement ofthe pawl nose with the rack teeth. This ratcheting lock configurationaccordingly provides the opposition required to hold objects in aflexion position, against opposable digits, and/or in the palm of theuser's hand.

It is often desirable for prosthetic digits to be lightweight, compact,strong, and include natural movement patterns. Digits configured inaccordance with the present technology can restore prehension in aperson with missing finger(s) or thumb by providing opposition to theintact digits such that object manipulation and stabilization may beperformed. The digit can exhibit a kinematic movement profile that isconducive to natural grasp patterns and provide opposition to forces inthe extension direction via a spring-loaded pawl and locking rackratchet mechanism, thereby allowing an individual to manipulate orstabilize objects. The digit may be spring-loaded in the extensiondirection by a torsion spring or other biasing member. The pawl may beautomatically disengaged from the rack when the digit reaches fullflexion, and the full flexion disengage stop may be adjustable. The pawlmay be automatically engaged with the rack when the digit reaches fullextension, and the extension stop may be adjustable. The pawl maycontain a lateral feature that creates interference with the anchoringlinkage under load and limits deflection of the structure. Practicalconsideration must also be given to the clinical socketing process,which determines the application of the digit to the user's hand via anintimately fitting mounting socket.

The digit can be moved to a new position by the user's opposing hand,other object, or by a routed tendon controlled by a more proximal jointor an external power source, among other movement options. The pawlmechanism and surrounding linkages can incorporate a toggle configuredto selectively disable the ratcheting function and put the digit into a“free motion” mode, such that the ratchet mechanism does not haltextension of the digit. In this regard, the digit can function as anadjustable opposition system or a driven digit to provide grasp patternssuch as the power hook, key, and cylindrical grasp, and other patternsand positions. The ability to perform these and other possible grasps isa portion of activities of daily living (ADL).

The terminology used in the description presented below is intended tobe interpreted in its broadest reasonable manner, even though it isbeing used in conjunction with a detailed description of certainspecific embodiments of the present technology. Certain terms may evenbe emphasized below; however, any terminology intended to be interpretedin any restricted manner will be overtly and specifically defined assuch in this Detailed Description section. Additionally, the presenttechnology can include other embodiments that are within the scope ofthe claims, but are not described in detail with respect to FIGS. 1-4B.

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structure or characteristicdescribed in connection with the embodiment is included in at least oneembodiment of the present technology. Thus, the appearances of thephrases “in one embodiment” or “in an embodiment” in various placesthroughout this specification are not necessarily all referring to thesame embodiment. Furthermore, the particular features or characteristicsmay be combined in any suitable manner in one or more embodiments.

B. Selected Embodiments of Prosthetic Digits

FIGS. 1A and 1B show elevation and perspective views, respectively, of athree-segment prosthetic digit 100 (“digit 100”) configured inaccordance with an embodiment of the present technology. The digit 100may be mounted to a rigid or flexible substrate for use by the user (notshown), which can include a socket (e.g., a partial hand socket,transradial socket, etc.) or frame. The substrate secures the digit 100to the user's hand in the approximate position of the user's anatomicdigits. In some embodiments, it is possible to mount the digit 100 in afashion that is non-anatomic, such as in the case of unique clinicalpresentations. The digit 100 generally includes an anchor piece 1configured to be affixed to or embedded in the user's socket, and a basepiece 2 of the digit 100 attached via fasteners or any other suitableattachment method. The digit 100 can be detached from the hand byremoving the base piece 2 from the anchor piece 1. The digit 100includes first, second, and third segments P1, P2, and P3, generallyrepresenting the bones of the finger, and the connections therebetweenrepresenting MCP, PIP, and DIP joints.

In the embodiment illustrated in FIGS. 1A and 1B, the digit 100 includesinstalled cosmetic and grip fairings 4 a and 5 a. The fairings 4 a and 5a may include sections having increased grip materials configured toincrease the friction of the fairings 4 a and 5 a. The fairing 4 a maybe mounted to the digit 100 by a fastener at a first mounting point 4 band the fairing 5 a may be mounted to the digit 100 by a fastener at asecond mounting point 5 c (see FIG. 2B, fasteners not shown). One ormore of the fairings 4 a and 5 a may include a relief cut 5 b to allowan extended range of articulation of the P2 and P3 portions of the digit100. These fairings may provide a silicone interface with objects forimproved grip and allow the user to select designs and colors, or toreplace these cosmetic pieces when wear occurs.

The anchor piece 1 may be configured to be attached to or embedded inthe user's stump interface (not shown), and may include featuresdesigned to allow for successful integration with a fabricated socket.The materials can be temperature resistant to withstand the exothermicepoxy reactions expected in socket fabrication. The anchor piece 1 mayalso include various slots, holes, and other attachment featuresintended to allow for successful integration with carbon fiber, epoxy,silicone, and other anchoring methods typically used in the prostheticsfield.

FIGS. 2A-2C show elevation, cross-section, and perspective views,respectively, of the prosthetic digit 100 of FIGS. 1A and 1B, still atfull extension, but with fairings 4 a and 5 a removed for sake ofillustration. The digit 100 may include a first pair of crossed linkages6 and 7 a via offset rotational joints A1, B1. The linkage 7 a, forexample, may comprise a plurality of rack teeth 7 b designed to engage apawl nose 3 b of pawl 3 a such that free motion is allowed in a flexiondirection (e.g., movement toward the position shown in FIGS. 3A-3C), anda structural position lock is created in the extension direction. Therack teeth 7 b are configured to interface with the pawl nose 3 a andmay be fabricated of hardened steel or other sufficiently strong andwear-resistant material(s). The pawl 3 a is connected in a rotationallypinned manner with a pin 11 to the linkage 6, and may beengaged/disengaged with the rack teeth 7 b via a spring-loaded detent 12a having a detent member 12 b (see FIG. 2B) installed on a proximalunderside of the pawl 3 a and in the linkage 6. In other embodiments,rack teeth are located on or coupled to any suitable linkage of thedigit 100 (e.g., linkages 6, 8, 9, 10, etc.), and in theseconfigurations, a pawl can be configured to interface with the rackteeth allow free motion in the flexion direction and positionally lockthe digit 100 in the extension direction.

The pawl 3 a can be movable between at least two positions via theproximal spring-loaded detent 12 a and 12 b: (a) engaged, such thatdetent member 12 b interfaces with an engaged surface 17 b of the pawl 3a; and (b) disengaged, such that detent member 12 b interfaces with adisengaged surface 17 c of the pawl 3 a. The engaged and disengagedsurfaces 17 b and 17 c are separated by a transition peak 17 apositioned to prevent the detent member 12 b from settling between theengaged and disengaged surfaces 17 b and 17 c. In some embodiments, oneor both of the engaged and disengaged surfaces 17 b and 17 c have aprofile shape of an Euler curve (e.g., as viewed in the orientation ofthe digit 100 in FIG. 2B) configured to minimize force variance of thedetent member 12 b on the pawl 3 a as the pawl 3 a rotates through arange of motion. In these configurations, the pressure variance isminimized by maintaining a substantially constant contact angle betweenthe detent member 12 b and the engaged surface 17 b and/or disengagedsurface 17 c.

To move the digit 100 in an extension direction, the pawl 3 a isdisengaged by moving the spring detent 12 a to the disengaged position,where the detent member 12 b interfaces with the disengaged surface 17c, thereby allowing the digit 100 to move freely toward extension bydisengaging the pawl nose 3 b from the rack teeth 7 b. In the disengagedposition, at full extension of the digit 100, the pawl 3 a is forcedback into the engaged position via a hard stop 14 (as best seen in FIG.2A).

The spring-loaded detent 12 a may be threaded and adjustable to accountfor tolerance stack ups. In the illustrated embodiments, for example,the spring-loaded detent 12 a comprises a spring-loaded round plungerthat deflects when pressed. The plunger surface slides over the proximalcurved portion (e.g., 17 b) of the pawl 3 a and acts as a detent,holding the pawl 3 a in the engaged or the disengage positions. Uponassembly, the spring detent linear position may be adjusted to anappropriate spring load corresponding to comfortable toggling betweenengaged and disengaged positions, and can be further adjusted to accountfor user preference, to correspond to particular installations, etc.

In some embodiments, the anchor piece 1 and base piece 2 may beconfigured such that only one attachment orientation between thecomponents is possible. In other embodiments, however, the componentshave various possible attachment orientations. The base piece 2 mayinclude a torsional spring 16 (see FIG. 3A) which exerts a constantextension-direction force on the system, acting to maintain the pawlnose 3 b in an interface position with the rack teeth 7 b and to returnthe system to extension when the pawl 3 a is disengaged from the rackteeth 7 b. The torsional spring 16, for example, may bias the digit 100toward the extended position shown in FIGS. 1A-2C. The torsional spring16 serves at least two purposes: (1) to force the pawl nose 3 b intoengagement with the rack teeth 7 b such that a posture is held afterbeing selected by the user; and (2) to automatically return the digit100 to extension when the pawl nose 3 b is disengaged from the rackteeth 7 b.

Referring to FIG. 2A, the digit 100 may further include linkages 8, 9,and 10, which form a portion of the coupled distal four-bar linkage(FIG. 2E) to interact with the proximal four-bar linkage (FIG. 2D) tocreate a relatively smooth, pleasing motion and kinematic space for thedigit 100 similar to an anatomic finger. The linkages 6, 7 a, 8, 9 and10, via rotational connections, form two four-bar linkages in series.FIGS. 2D and 2E show elevation views of rotational connections ofproximal and distal four-bar linkages, respectively, of the digit 100.FIG. 2D, for example, shows the rotational connections of the proximalfour-bar linkage of the segment P1. The proximal four-bar linkage of thesegment P1 is rotatably coupled to the base piece 2 at a rotationalconnection A1 and a rotational connection B1. As the digit 100transitions from full extension (FIGS. 2A-2C) to full flexion (FIGS.3A-3C), the linkages 6 and 7 a rotate clockwise (direction CW in FIGS.2D and 2E; counterclockwise direction CCW) about the rotationalconnections A1 and B 1. During such clockwise rotation, the linkages 6and 7 a rotate oppositely relative to each other about the pin 11. Therelative rotation of the linkages 6 and 7 a about the pin 11 causes arotational connection B2 to move in a clockwise orbital path relative toa rotational connection A2 and spread apart from each other.

FIG. 2E shows rotational connections of the distal four-bar linkage ofthe segment P2. The distal four-bar linkage of the segment P2 isrotatably coupled to the proximal four-bar linkage of the segment P1 atrotational connections A2 and B2. During the rotation from fullextension toward full flexion described above, the rotational connectionB2 orbits clockwise around and spreads apart from the rotationalconnection A2 and causes the linkage 8 to rotate in a clockwisedirection about a rotational connection B3 relative to at least thelinkages 6 and 7 a. Such rotation causes clockwise rotation of thelinkage 9 about the rotational connection B2 with respect to the linkage6. As the linkage 8 rotates clockwise, the linkage 10 also rotatesclockwise with respect to the rotational connection B3, and further, therelative movement of the linkages 9 and 10 cause an opposite rotation ofthe linkages 9 and 10 about a rotational connection D, which in turnresults in a clockwise rotation of the linkage 10 about a rotationalconnection T. The rotational positions of the linkages of the segmentsP1 and P2 described above can be further understood by comparing theposition of the components in FIG. 2B with the position of thecomponents in FIG. 3C.

The prosthetic digit 100 opposes extension movement, allowing objects tobe gripped and manipulated to hold objects in a flexion position,against opposable digit 100 s, and/or in the palm of the hand. Apowerful orientation for the prosthesis is the “power hook grasp.” Thisgrasp position is utilized in such ADLs as lifting a bucket of water bythe handle, or carrying a plastic grocery bag, among other ADLs. Theposture required to achieve the power hook grasp occurs when the pawl isengaged at an intermediate position on the rack of teeth (e.g., aposition intermediate of the positions in FIGS. 2A-2C (full extensionwith adjustability) and FIGS. 3A-3C (full flexion with adjustability)).When the digit 100 is loaded in the power hook grasp position, theproximal linkages 6 and 7 a have forces tending to move them closertogether as the device deflects toward an extended position. Thisconfiguration puts a compression load on the nose of the pawl 3 b, whichcauses a resulting double-shear load on the press fit pin 11, tending tofix the pawl 3 a to the linkage 6.

The aforementioned power hook grasp loading configuration can also causea spreading deformation between the linkages 6 and 7 a and force thenose of the pawl 3 b in a proximal direction away from the rack teeth 7b. At a certain deformation levels, the pawl 3 a may over-toggle andflip, such that the nose 3 b moves proximally and loses purchase on therack teeth 7 b, resulting in failure of the mechanism, and potentialdamage to components. To prevent such overtoggling, the pawl 3 a mayinclude one or more pawl dogs 15 to reduce the deflection between thelinkages 6 and 7 a, and to increase the load bearing capability of thedigit 100. In one example of testing the digit 100 in the power hookgrasp, the load capacity of the digit 100 increased by −300% with theaddition of the pawl dogs 15. The pawl dogs 15 interface with theanchoring linkage 6 such that, when under deflection due to load, thepawl dogs 15 contact the sides of the anchoring linkage 6 whichredirects the load into a lower deflection condition between thelinkages 6 and 7 and prevents the aforementioned pawl overtoggle,consequently increasing the load capacity of the digit 100.

FIGS. 3A-3C show perspective, elevation, and cross-section views,respectively, of the prosthetic digit 100 of FIGS. 1A and 1B at fullflexion, with fairings 4 and 5 removed for sake of illustration. At theposition of full flexion, an adjustable hard stop 13 forces the pawl 3 ainto the disengage position, where the detent member 12 b interfaceswith the disengage surface 17 c. The hard stop 13 allows a user to fullyflex the digit 100 via a tabletop, opposing hand, or other object, andreturn it to an extension position (shown in FIGS. 1A-2C) via thetorsional spring 16. The full flexion hard stop 13 may be adjustable,thereby allowing for variation in socket fabrication and fingerplacement. For example, if a clinical technician over-rotates the digit100 toward the palm of the user's hand when embedding the anchor piece 1in the socket, the digit 100 may be unable to achieve a non-adjustablefull flexion hard stop disengage point due to the tip of the mechanismimpacting the user's palm prematurely. The adjustability of the fullflexion hard stop 13 allows for the functionality to be available, evenin the case of poor positioning by a clinical technician. In oneembodiment, the full flexion hard stop 13 is a set screw embedded intothe rack linkage 7 a. The position of the set screw 13 within the racklinkage 7 a can be adjusted to change the pawl 3 a disengage point.Other embodiments are possible for the adjustable full flexion hard stop13 and are also within the scope of the present disclosure.

Similar adjustability may be provided for the extension pawl engagefeature 14. In this regard, if a technician inadvertently over-rotatesthe position of the anchor toward the dorsum of the hand, the digit 100would have a hyperextended neutral position, which is an impediment tofunction of the prosthesis device. The extension pawl engage feature 14can be adjusted such that pawl 3 a engagement is forced sooner than fullextension to prevent the digit 100 from returning to a functionallyimpaired, hyperextended neutral position. As noted above, in otherembodiments, the rack teeth are located on a different linkage of thedigit 100, such as the linkage 8, 9, 10, etc., and the pawl, hard stop,and extension pawl engage feature can be positioned to interface withthe rack teeth on a different linkage.

Embodiments of the present technology are expected to provide a numberof advantages over conventional devices including, among otheradvantages: (1) lower weight; (2) integration of the rack and pawl intoa proximal four-bar configuration where forces are relatively low; (3)the full flexion pawl disengage is adjustable, allowing for adjustmentswhen poor placement occurs during mounting socket fabrication; (4) theextension pawl engage is adjustable, allowing for adjustments when poorplacement occurs during mounting socket fabrication; (5) the pawl dogfeature is engaged during high loads and deflection, acting to lessendeflection and increase the load bearing capability of the device; and(6) attachment points for consumable cosmetic covers including aestheticfeatures and functional gripping features for improved objectmanipulation. The embodiments are also suitable for dynamictendon-driven digits. As compared with conventional prosthesis digittechnology, the present technology is further expected to provideenhanced application robustness, cosmetic appeal, and serviceability.

FIGS. 4A and 4B show elevation views of a two-segment prosthetic digit200 (“digit 200”) having a similar configuration of the proximalfour-bar linkage of the digit 100, including an anchor 1′ and linkages2′, 6′, 7′, and 8′, but eliminating the linkages 9 and 10 of the digit100. The digit 200 provides a fixed distal joint and only one four-barlinkage, and may include fairings 20′ and 21′ configured to functionsimilarly to fairings 4 a and 5 a of the digit 100. Some components ofthe digit 200 are similar to those of the digit 100, but are denotedwith a prime (e.g., 2′, 3′, etc.) for the digit 200. Like referencenumerals of the digit 200 in FIGS. 4A and 4B to those of the digit 100in FIGS. 1-3C, should not necessarily be construed as the exact samecomponent, and the components in FIGS. 4A and 4B may differ in shape,size, function, etc. to those in FIGS. 1-3C.

Referring to FIG. 4B, the extension pawl 3 a′ engage feature is amechanical stop 18′ on the base piece 2′ that impacts the pawl 3 a′ onthe bottom of its paddle at extension and forces the detent member 12 b′into engagement with the surface 17 b′. In another embodiment, asdescribed above, the extension pawl engage feature is mechanical stop14′ positioned at the distal end of the pawl 3 a′ and configured toengage the dorsal surface of the pawl nose 3 b′ or pawl dogs 15′ toforce the detent member 12 b′ into engagement with the surface 17 b′. Insome embodiments, the extension hard stop 14′ is adjustable, such as byusing an adjustable stop 19′. In other embodiments, the extension pawlengage feature may have a different arrangement and/or include differentfeatures. Both the adjustable full flexion hard stop and the adjustableextension pawl engage features can reduce the usable range of teeth onthe rack 7 b′ to customize the digit 100 to an individual user.

In some embodiments, the pawl 3 a′ may have a paddle portion on thedorsal side to allow a user to manually disengage the ratchet mechanism(the pawl nose 3 b′ and the rack teeth 7 b′). The paddle portion can beplaced in various locations and still allow for a manual disengagementof the ratchet lock. The bottom surface of the pawl 3 a′ is configuredto engage with the adjustable full flexion hard stop 13′ such that atfull flexion the pawl 3 a′ will be forced into a disengaged position andwill return the structure to full extension via the spring forcegenerated by the torsional spring 16′. The dorsal surface of the nose ofthe pawl is designed with a feature that interfaces with the adjustableextension engage feature 14′ to return the pawl 3 a′ to the engagedposition at full extension, e.g., the pawl dogs 15′.

The present technology may utilize two or three pairs of offsetrotational joints, connected via rigid linkages, to generate coupledfour-bar movement and to mimic the sliding condylar motion seen innatural anatomy, providing a compact and realistic motion space. In theembodiments of the digit 100 described above with reference to FIGS.1A-3C, segments P1, P2, and P3 represent the bones of the finger and theconnections therebetween represent the MCP, PIP, and DIP joints. In theembodiments of the digit 200 described above with reference to FIGS. 4Aand 4B, segments P1 and P2 represent the bones of the finger and theconnections therebetween represent only the MCP and PIP joints, with afixed DIP joint. Other configurations are also within the scope of thepresent disclosure.

C. Conclusion

The above detailed descriptions of embodiments of the technology are notintended to be exhaustive or to limit the technology to the precise formdisclosed above. Although specific embodiments of, and examples for, thetechnology are described above for illustrative purposes, variousequivalent modifications are possible within the scope of thetechnology, as those skilled in the relevant art will recognize. Forexample, while steps are presented in a given order, alternativeembodiments may perform steps in a different order. Moreover, thevarious embodiments described herein may also be combined to providefurther embodiments. Reference herein to “one embodiment,” “anembodiment,” or similar formulations means that a particular feature,structure, operation, or characteristic described in connection with theembodiment can be included in at least one embodiment of the presenttechnology. Thus, the appearances of such phrases or formulations hereinare not necessarily all referring to the same embodiment.

For ease of reference, identical reference numbers are used to identifysimilar or analogous components or features throughout this disclosure,but the use of the same reference number does not imply that thefeatures should be construed to be identical. Indeed, in many examplesdescribed herein, identically numbered features have a plurality ofembodiments that are distinct in structure and/or function from eachother. Furthermore, the same shading may be used to indicate materialsin cross section that can be compositionally similar, but the use of thesame shading does not imply that the materials should be construed to beidentical unless specifically noted herein.

Moreover, unless the word “or” is expressly limited to mean only asingle item exclusive from the other items in reference to a list of twoor more items, then the use of “or” in such a list is to be interpretedas including (a) any single item in the list, (b) all of the items inthe list, or (c) any combination of the items in the list. Where thecontext permits, singular or plural terms may also include the plural orsingular term, respectively. Additionally, the term “comprising” is usedthroughout to mean including at least the recited feature(s) such thatany greater number of the same feature and/or additional types of otherfeatures are not precluded. Directional terms, such as “upper,” “lower,”“front,” “back,” “vertical,” and “horizontal,” may be used herein toexpress and clarify the relationship between various elements. It shouldbe understood that such terms do not denote absolute orientation.Further, while advantages associated with certain embodiments of thetechnology have been described in the context of those embodiments,other embodiments may also exhibit such advantages, and not allembodiments need necessarily exhibit such advantages to fall within thescope of the technology. Accordingly, the disclosure and associatedtechnology can encompass other embodiments not expressly shown ordescribed herein.

1-23. (canceled)
 24. A prosthetic digit, comprising: a first linkagecoupled to a base, wherein the first linkage comprises a plurality ofrack teeth; a second linkage coupled to the base in an overlappingarrangement with the first linkage, wherein the first linkage and secondlinkage are each configured to pivotably with respect to the base duringflexion and/or extension of the prosthetic digit; and a pawl operablycoupled to the second linkage, wherein the pawl is movable between— anengaged position in which a distal nose of the pawl abuts one of theplurality of rack teeth, and a disengaged position in which the distalnose is spaced away from and does not contact the rack teeth duringflexion and/or extension of the prosthetic digit.
 25. The prostheticdigit of claim 24, further comprising a third linkage pivotably coupledto a distal end of the first linkage, wherein the third linkage comprisea stop surface, and wherein the pawl is configured to abut the stopsurface to return the pawl to the engaged position.
 26. The prostheticdigit of claim 24, further comprising a pawl dog, and wherein, when thepawl is in the engaged position, the pawl dog extende from the distalnose of the pawl to engage a side of the first linkage.
 27. Theprosthetic digit of claim 26 wherein the pawl dog is configured tocontact the first linkage during loaded articulation of the prostheticdigit.
 28. The prosthetic digit of claim 24, further comprising: a thirdlinkage pivotably coupled to the base and a proximal end of the firstlinkage; and a fourth linkage pivotably coupled to the base and aproximal end of the second linkage.
 29. The prosthetic digit of claim 28wherein pivotable movement of the first elongate linkage in a firstdirection with respect to the base causes pivotable movement of thethird elongate linkage in a second, opposite direction.
 30. Theprosthetic digit of claim 24 wherein the first linkage and secondlinkage are pivotably coupled to the base.
 31. The prosthetic digit ofclaim 24, further comprising an anchor configured to to be affixed to orembedded in a socket of a user's hand, and wherein the base is fixedlycoupled to the anchor.
 32. The prosthetic digit of claim 24, furthercomprising a biasing member positioned to rotationally urge a distal endof one of the first and second linkages toward a distal end of the otherof the first and second linkages.
 33. The prosthetic digit of claim 32wherein the biasing member is positioned to urge the prosthetic digittoward an extended position, abutting the distal nose against one of theplurality of the rack teeth in the engaged position of the pawl.
 34. Theprosthetic digit of claim 33, further comprising an adjustable flexionmember carried by the first linkage, wherein the adjustable flexionmember is positioned to rotate the pawl to the disengaged position whenthe prosthetic digit reaches a set maximum flexion position.
 35. Theprosthetic digit of claim 24, further comprising an adjustable extensionmember configured to abut a surface to limit the rotation of theprosthetic digit at a maximum extension position.
 36. The prostheticdigit of claim 24, further comprising a detent member configured tocontact one of (a) a concave disengaged surface on the pawl to retainthe pawl in the disengaged position and (b) a convex engaged surface onthe pawl to retain the pawl in the engaged position.
 37. The prostheticdigit of claim 24, further comprising a fairing coupled to and coveringat least a portion of the first linkage and the second linkage.